Seafloor May Help Unlock Quake, Tsunami Mysteries

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Seismic monitoring and centuries of experience have given
humankind a pretty good idea of what areas are prone to the
devastation of earthquakes and tsunamis. But to truly prepare for
huge temblors and accompanying tsunamis like the one that ravaged
Japan in March, we need to take a closer look at the deep
seafloor, according to one geophysicist.

Writing in the journal Nature this week, Georgia Institute of
Technology earthquake researcher Andrew Newman argues for an
international effort to monitor the deep seafloor for signs of
"locked patches" on faults, where two creeping masses of land
catch against one another, storing energy until they break,
unleashing
an earthquake. These monitoring efforts wouldn't predict
exactly when earthquakes would happen, but they would help us
gauge how large an impending disaster might be, Newman said.

"Essentially, what we need to start being able to do is identify
exactly how the offshore environment is really locking up for
earthquakes," Newman told LiveScience. "We can see a little bit
of that by using data that's just on land. But [we] just don't
have the resolution offshore that we need."

Watching the trench

The size of Japan's March 11 quake
surprised scientists, who hadn't expected that area of the
Japan Trench to generate a magnitude-9.0 temblor. In retrospect,
California Institute of Technology geophysicist Hiroo Kanamori
told LiveScience's sister site, OurAmazingPlanet.com, in April
that GPS monitors along the Japan trench did show signs that
large amounts of strain were building along the fault. But for a
rare event like the 9.0-magnitude quake, Kanamori said,
scientists do not have enough data to assess the hazards.
[ In
Pictures: Japan Quake and Tsunami ]

And Japan is one of the best performers in terms of the number of
seismic monitors on the deep seafloor, Newman said.

Land-based seismic monitoring can capture what's happening on the
seafloor out to a distance of about 12 to 24 miles (20 to 40
kilometers), Newman said. But faults can rupture 125 miles (200
km) offshore in deep ocean trenches, where monitors are rare.
Besides Japan, Newman said, only offshore Peru has significant
seafloor monitoring.

With better monitoring, he wrote, scientists can make more
accurate predictions about how big an earthquake and ensuing
tsunami might be. In Japan's case, for example, the walls around
the
Fukushima nuclear plant might have been built higher,
preventing a nuclear disaster second only to Chernobyl.

Cutting the cost

Monitoring the deep seafloor isn't a simple prospect, however.
Right now, ships place transponders on the seafloor and then read
the signals, triangulating the transponders' position and any
movement since the last check. Just one position check can cost
$500,000, Newman wrote, and many data points over time are
necessary to determine what a fault is doing.

To expand the undersea seismic network, Newman said, researchers
need to develop autonomous sensor systems that will send
information back to shore via undersea cables or buoys, negating
the need for ships. In the Japan Trench, Newman wrote, another
100 to 400 sensors are needed. For larger networks, scientists
could deploy a sensor every 3,100 to 9,300 miles (5,000 to 15,000
km), he said.

Seismic monitoring isn't cheap: The land-based network monitoring
the plate boundary along the U.S. West Coast cost $100 million to
install and $10 million to maintain each year. But with
technological advances, Newman wrote, it should be possible to
equip an environment like the Japan Trench with a seismic network
for between $5 million and $20 million — a paltry sum compared
with the projected $300 billion
cost of the Japan disaster.

"It's ambitious," Newman said. "But I don't think it's out of the
realm of possibility."